The invention relates to a slit closure valve for container openings or the like. The invention especially relates to self-closing and self-opening valves for installation in an opening of a container or for completing a closure cap.
A one-piece slit closure valve, which can be produced in a single operational step by a two component injection moulding process using different thermoplastic plastics materials is known (c.f. e.g. EP-A-0 743 259). The substantial manufacturing advantages attained hereby are however countered by the fact that the restoration to its original configuration of a container provided with such a valve, after the container has been compressed so as to exert pressure on the contents of the container, is frequently incomplete, or, only occurs after a long period of time since the pressure between the interior of the container and its surroundings cannot equalise. Thus various alternative designs of self-closing valves incorporating a pressure equalising function have already been proposed (c.f. e.g. DE-U-298 17 571, 298 18 414). A specially designed and arranged closure element for closing an outlet opening which has no slit is necessary for performing the pressure equalising function. The advantage of such a specific pressure equalising arrangement is thereby obtained at the expense of a valve which is less convenient to manufacture.
Hence, there is an object of the invention to provide a slit closure valve of the type described hereinabove which has a pressure equalising function and, at the same time, is of simple construction. It is another object of the invention to provide a slit closure valve of the type described hereinabove which can be formed, ready for use, in a single operational step.
The above objects and other objects of the invention which will become apparent hereinafter are achieved by a slit closure valve including a membrane member of flexible material having an at least unidirectionally aligned slit-like outlet opening, and a base member peripherally surrounding the membrane member. The base member is connected to the membrane member and said outlet opening held in a closed position by the resilient properties of the material and adapted to be moved into an open position against the resilient bias force of the material by a predetermined differential positive pressure exerted on one side of the membrane member. A peripheral wall portion of the base member and an ad acent wall portion of the membrane member include therebetween an acute angle of less than 90xe2x80x2, and at least one further substantially peripherally aligned slit-like passage opening held in a closed position by the resilient properties of the material is provided in the membrane wall portion near the base member. The passage opening can be moved into a releasing position by a differential negative pressure exerted on the membrane member from the side subjected to said predetermined differential positive pressure.
Accordingly, the slit closure valve is constructed such that a wall portion of a membrane member is connected to a base member at an acute angle. One or more slit-like passage openings are provided in the area of the joint section. The purpose of these passage openings is to produce an equalisation of the pressure by enabling the surrounding air to enter into the interior of the container when negative pressure conditions exist therein. By contrast, the slit-like passage openings are kept closed when there is an positive pressure in the interior of the container so that this positive pressure can only be expressed by releasing the slit-like outlet opening at an e.g. central portion of the membrane member. The slit closure valve of the invention is of particularly simple and uncomplicated construction and it can be manufactured economically together with said openings in a single operational step e.g. by injection moulding. An embodiment of the slit closure valve lending further assistance to the manufacturing process whilst simultaneously improving the above-mentioned functions provides for the membrane member to have a peak-roofed configuration. Further embodiments of the invention are mentioned in the claims.